This invention relates generally to spark protection circuits and particularly to spark gaps for use in television receivers or the like.
As is well known, television receivers include cathode ray tubes (CRT's) which have closely spaced electrodes operated in an evacuated atmosphere in close proximity to very high DC potentials. In a typical television receiver, for example, the high voltage electrode in the CRT may carry a potential on the order of 25,000 volts or more. Because of the nature of CRT's and their manufacturing process, it is impossible to completely eliminate all foreign particles. Occasionally, a particle may be dislodged and cause a high voltage breakdown between electrodes in the tube. Because of the substantial capacitance in the system, a high energy arc occurs. It is therefore essential to protect the delicate circuits and components connected to the CRT electrodes, as well as some of the CRT electrodes from the effects of such high voltage discharges. It is customary to use spark gaps for this purpose.
Conventional spark gaps comprise a pair of discharge electrodes separated by an air space, with one electrode being connected to a good ground. Other types of spark gaps, such as those of the enclosed variety have also been used, but those employing air gaps have generally been preferable, both from cost and reliability standpoints.
All spark gaps are prone to deterioration and eventual failure if subjected to repeated discharges. If heavy currents begin to melt and displace metal or deposit burned materials in the arcing area, the life of the spark gap is very seriously affected. Failure of the spark gap often results in follow-through current after discharge of the arc energy, which can destroy the very circuits and components the spark gap is intended to protect. Ideally, the spark gap will be capable of carrying heavy arc currents without deterioration and be capable of rapidly dissipating the arc energy to minimize the follow through effects of the arc.
A well known arc discharge mechanism, often used in connection with utility power line equipment, is sometimes referred to as the "Jacob's Ladder", because of its climbing effect in "blowing" out the arc. With it a pair of heavy electrodes or "arcing horns" is positioned in divergent relationship to each other. Thus, at their lower portions where the arc is initiated, they are fairly close to each other whereas at their upper portions they are much farther apart. The horns are oriented in the vertical direction so that the heated gases generated by the arc in the air tends to force or blow the arc upward along the diverging arcing horns until a point is reached where the arc cannot sustain itself because of the arc length between the arcing points. A similar arrangement is used in power line switches, for example where there is usually a very substantial residual current that is interrupted when a switch is opened. In that environment, the arcing horns protect the switch contacts by carrying the residual current when the switch is opened. Thereafter, depending upon the design, the horns are drawn apart by continued movement of the switch parts and the "Jacob's Ladder" effect may be used to help extinguish the arc.
The invention consists of a "Jacob's Ladder" arrangement in a very convenient and attractive spark gap for use in television receivers or the like.